The free databases below are for those looking for H-1B visa sponsors and other relevant information:
Federal labor site - Extremely long list of companies that have filed a Labor Condition Application, which is commonly used as evidence for a H-1B visa petition. Special Feature: Downloadable in Access format.
Myvisajobs.com-- Lists companies and institutions that have hired people with green cards and H1-B Visas. Relevant metrics include ranking, number of people hired, and salary information.